There have been widely used computerized numerically controlled (CNC) laser beam machining apparatus composed of a laser oscillator and a computerized numerical control (CNC) system. Particularly, the high-speed machining capability of a laser beam machining apparatus and the complex profile control of a CNC system are coupled to each other for the high-speed machining of a complex configuration in a non-contact fashion. CNC laser beam machining apparatus, in particular, capable of three-dimensional machining that cannot be performed by conventional punch presses, nibbling machines, or the like have been put to practical use.
For three-dimensionally machining a workpiece on a CNC laser beam machining apparatus, it is necessary to control X-, Y-, and Z-axes and also to control the attitude of a nozzle on the tip end of a hand. The control axes use for the control of the attitude of the nozzle are referred to as .alpha.- and .beta.-axes. There are two types of nozzle head mechanisms, described below, for controlling the attitude of a nozzle.
The first type of nozzle head mechanism is known as a zero-offset or one-point-oriented type nozzle head mechanism that has an .alpha.-axis as a rotational axis with respect to a Z-axis, and a .beta.-axis as a rotational axis inclined with respect to the Z-axis.
The second type of nozzle head mechanism is referred to as an offset type nozzle head mechanism that has an .alpha.-axis as a rotational axis with respect to a Z-axis, and a .beta.-axis as a rotational axis perpendicular to the Z-axis.
The zero-offset type nozzle head mechanism is complex in mechanism structure, but can be controlled easily and is preferable from the standpoint of nozzle control since the position of the tip end of the nozzle remains unchanged even when the positions of the X-, Y-, and Z-axes change. One attitude control system for a CNC laser beam machining apparatus with a zero-offset type nozzle head mechanism is disclosed in Japanese Laid-Open Patent Publication No. 1-162592 filed by the applicant.
The offset type nozzle head mechanism requires a complex control process and is not suitable for high-speed machining though the mechanism structure is simple. Japanese Laid-Open Patent Publication No. 1-22419 filed by the applicant discloses a system for controlling the attitude of an offset type nozzle.
In either type of nozzle head mechanism, however, when the components rotate about the .alpha.-axis, they also rotate about the .beta.-axis. Since the components are rotated about the .beta.-axis by the rotation about the .alpha.-axis, it is necessary to compensate for the corotation about the .beta.-axis. Particularly, for such corotation compensation, the gear ratio of gears which couple vertical and horizontal shafts for the .beta.-axis is limited to 1:1. This has posed problems with respect to the service life and mechanical strength of the gears.